My OperaSan Diego, Santa Ana and Wildfires
Friday, October 26, 2007 9:28:26 AM
She starts when masses of cold air and accompanying high pressure form over the Great Basin in Utah and Nevada East of the Sierra Nevada Mountains. The air circulates clockwise around the high pressure area bringing winds from the east and Northeast to Southern California (the reverse of the westerly winds characteristic of the latitude). Some call her the Santa Ana. Others call her the Devil's Breath.
The Santa Ana winds usually form during autumn and early spring when the desert is relatively cold, although they may form at virtually any time of year. When the winds are moderate, they blow air pollution out to sea and make life in Southern California more pleasant. This week they have been blowing at near record speeds. They grow warmer, dryer and stronger as they spill south and west, falling several kilometres down through mountain canyons towards the ocean. The southern California coastal region gets some of its hottest weather of the year during autumn while Santa Ana winds are blowing. During Santa Ana conditions it is typically hotter along the coast than in the deserts and the humidity plummets to less than 15%.
On the satellite image there are no clouds. The weather is clearly dry. Large smoke plumes are driven from the large wildfires (red spots) towards the west far out over the Pacific Ocean by strong winds. Wind speeds as high as around 160 km/hr were measured in a couple of areas. That is the speed of winds in a Category 2 hurricane.
In Europe we know this type of winds from the Alps (the Föhn), but it is also found in other parts of the world (under different names):
* Zonda winds in Argentina
* Chinook winds in the Rocky Mountains, United States/Canada and the Chugach Mountains of Alaska, United States
* Diablo winds in the San Francisco Bay Area, United States
* The Nor'wester in Canterbury and Otago, New Zealand
* Halny in the Carpathian Mountains, Eastern Europe
* Fogony in the Catalan Pyrenees
* Bergwind in South Africa
* Viento Sur in the Cantabrian region (northern Spain)
* Terral in Málaga (southern Spain)
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* http://www.npr.org/templates/story/story.php?storyId=15584420
* http://en.wikipedia.org/wiki/Santa_Ana_wind
Find below a diagram showing the principles of the Föhn winds, with description underneath.
Moist air is forced to rise over the mountains. Condensation produces thick clouds and the air cools slowly at 0.5°C/100m. Heavy rain falls over the mountains and the air loses most of its moisture content. On the other side of the mountains the now dry air descends and warms up at 1°C/100m. The wind speed increases.
The Santa Ana winds usually form during autumn and early spring when the desert is relatively cold, although they may form at virtually any time of year. When the winds are moderate, they blow air pollution out to sea and make life in Southern California more pleasant. This week they have been blowing at near record speeds. They grow warmer, dryer and stronger as they spill south and west, falling several kilometres down through mountain canyons towards the ocean. The southern California coastal region gets some of its hottest weather of the year during autumn while Santa Ana winds are blowing. During Santa Ana conditions it is typically hotter along the coast than in the deserts and the humidity plummets to less than 15%.
On the satellite image there are no clouds. The weather is clearly dry. Large smoke plumes are driven from the large wildfires (red spots) towards the west far out over the Pacific Ocean by strong winds. Wind speeds as high as around 160 km/hr were measured in a couple of areas. That is the speed of winds in a Category 2 hurricane.In Europe we know this type of winds from the Alps (the Föhn), but it is also found in other parts of the world (under different names):
* Zonda winds in Argentina
* Chinook winds in the Rocky Mountains, United States/Canada and the Chugach Mountains of Alaska, United States
* Diablo winds in the San Francisco Bay Area, United States
* The Nor'wester in Canterbury and Otago, New Zealand
* Halny in the Carpathian Mountains, Eastern Europe
* Fogony in the Catalan Pyrenees
* Bergwind in South Africa
* Viento Sur in the Cantabrian region (northern Spain)
* Terral in Málaga (southern Spain)
-----------
* http://www.npr.org/templates/story/story.php?storyId=15584420
* http://en.wikipedia.org/wiki/Santa_Ana_wind
Find below a diagram showing the principles of the Föhn winds, with description underneath.
Moist air is forced to rise over the mountains. Condensation produces thick clouds and the air cools slowly at 0.5°C/100m. Heavy rain falls over the mountains and the air loses most of its moisture content. On the other side of the mountains the now dry air descends and warms up at 1°C/100m. The wind speed increases.
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